This invention relates in general to printers of the type for automatic printing of letters and numerals for setting forth production dates, weights, prices, and the like on continuously fed wrapping film, as of synthetic resin and the like, and, more particularly, to an improvement in a printer of the hot-roll type adapted for heating the printing roll. A hot-roll printer incorporating a printing roll with printing type heated to a temperature of between 120.degree. C. to 150.degree. C. with the surface of the type being inked through contact with an ink roll for reliable and clear printing upon a suitable printing material, such as continuously fed synthetic resin film, has been set forth an described in Japanese Utility Model No. 45154/1983 having been filed by the present inventor. In a printer of such type it is necessary to embody a structure wherein the printing part can rotate while being heated by heater element since the printing operation is effected by rotation of a printing roll.
In the aforesaid utility model application the inventor has disclosed a hot-roll printer wherein an electric heater is installed within the printing roll which constitutes a printing part. Therein, in order to provide electricity to the heater element it was necessary to present, on the rotating side, a slip-ring to connect with the heater element, and, on the fixed side, a brush to contact with the slip-ring. In addition to providing an electricity feeding mechanism of such type, the same has caused a further problem by necessitating an increase in the axial dimension of the printing part, thus enhancing its size. Furthermore, the electrical contact between the slip ring and the brush is apt to become unreliable during usage which is clearly a serious disadvantage to securing a stable supply of electricity and assuring of maintaining the printing part in reliable condition. Still further, as the heating element in such structure effects its cycle of rotation and stopping with the printing roll, the leads are apt to break because of vibration developed during rotation so that the same become inoperative in a reasonably short period.
A further drawback of this prior art structure is the difficulty in securing to the printing roll a thermo-sensor for maintaining the heating temperature consistent within the range of 120.degree. C. to 150.degree. C. so that it is substantially impossible to assure of accurate temperature.
In the structure set forth in the above identified utility model application the clutch-brake unit and the encoder of the printer are formed separately and necessitate a large space for the mounting thereof with there also being required rotation transmission means between the encoder and the power supply shaft. All of this further conduces to a substantially enlarged printer. The clutch-brake unit and the encoder are thus of a size out of proportion with respect to the relatively small character of the hot-roll printer and thus detract from the design of the device.
In the operation of printers of this type it is requisite to maintain the ink roll warm in order to maintain the fluidity of the absorbed ink. The surface of the printing type set on the printing roll is frequently non-uniform and uneven. In most cases the lack of uniformity of the type surface is due to an error in either molding or securement and thus the amount of ink to be applied to the type varies depending upon the size, thickness and nature of the letter of the type, or upon various outer dimensions of the ink roll. Therefore, it is preferable that a printing device have a means to enable a fine adjustment of the distance between the ink roll and the type.
Furthermore, the prior art structure as set forth in the aforesaid utility model application, although being provided with a mechanism for such a fine adjustment, is one that is of a complicated link structure and prone to breakdown in the portions supporting the ink roll. Accordingly, there is a problem of providing a fine adjustment that can be effected accurately betwen the ink roll and the printing type.
Accordingly, it is the primary object of the present invention to solve the numerous problems above enumerated with respect to the prior art structure.
Another object is to provide a printer which does not require the supply of electricity by means of a slip ring so that the printing part may be of relatively reduced size and more readily maintainable.
Another object of the present invention is to provide a printer wherein the life of the heater may be relatively prolonged and the thermal control for the printing part easily effected.
It is still another object of the present invention to provide a printer wherein a unitary compact mechanism may be provided for inclusion of the clutch brake unit and an encoder which conduces to substantial reduction in the overall size of the printer.
It is a still further object of the present invention to provide a printer wherein a fine adjustment of the distance between the ink roll and the printing roll type can be accurately achieved and with the ink roll being supported in a stable fashion by a simple supporting mechanism.